Which foam expansion category ranges from 20:1 to 200:1 and is used to suppress vapors from hazardous materials spills at expansion ratios such as 30:1 and 55:1?

• A. Low expansion ratio
• B. Medium expansion ratio
• C. High expansion ratio
• D. Ultra expansion ratio

Answer: (B)

Foam expansion categories describe how much air is mixed into the foam to create a protective blanket. The range from 20:1 to 200:1 is defined as medium expansion in this material, and it’s used to suppress vapors from hazardous-material spills because it forms a broad, stable foam blanket over the spill that cools and seals vapors without needing excessive water. The expansion ratios given—30:1 and 55:1—fall within that range, demonstrating how medium expansion provides enough coverage to blanket a spill area while maintaining foam durability. Higher expansion foams would be too light for good vapor suppression on a spill, and low expansion foams are denser with less surface reach. So this expansion level offers the right balance for vapor suppression, making it the appropriate choice.